1. Field of the Invention
The present invention relates to a fuel cell stack formed by stacking a plurality of fuel cells together. Each of the fuel cells is formed by stacking a membrane electrode assembly and separators together. The membrane electrode assembly includes a pair of electrodes and an electrolyte membrane interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane. The electrolyte membrane is a polymer ion exchange membrane. In the fuel cell, the electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly is sandwiched between a pair of separators to form a unit cell. In use, in the fuel cell of this type, generally, a predetermined number of unit cells are stacked together to form a fuel cell stack, e.g., mounted in a vehicle.
In the fuel cell, a fuel gas flow field is formed in a surface of one separator facing the anode for supplying a fuel gas to the anode, and an oxygen-containing gas flow field is formed in a surface of the other separator facing the cathode for supplying an oxygen-containing gas to the cathode. Further, a coolant flow field is formed between the adjacent separators of the fuel cells for supplying a coolant within electrode areas along surfaces of the separators.
Further, mostly, the fuel cell of this type adopts so called internal manifold structure in which a fuel gas supply passage and a fuel gas discharge passage, an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage, and a coolant supply passage and a coolant discharge passage are formed in the fuel cell for allowing the fuel gas, the oxygen-containing gas, and the coolant to flow through the unit cells in the stacking direction.
For example, a fuel cell stack disclosed in International Publication No. WO 2010/082589 is formed by stacking an electrolyte electrode assembly and metal separators. The electrolyte electrode assembly includes a pair of electrodes and an electrolyte interposed between the electrodes. Each of the metal separators has rectangular surfaces. The metal separator has a power generation unit including a corrugated gas flow field on its surface facing the electrode for supplying the fuel gas or the oxygen-containing gas as a reactant gas along the electrode. Power generation units are stacked together such that a coolant flow field is formed between the power generation units on a back surface of the corrugated gas flow field.
A reactant gas supply passage and a reactant gas discharge passage as passages of the reactant gas extend through opposite two sides of the metal separators. A pair of coolant supply passages and a pair of coolant discharge passages as passages of the coolant extend through the other opposite two sides of the metal separators, at least adjacent to the reactant gas supply passage or the reactant gas discharge passage, separately on the respective sides.
Since the pair of coolant supply passages are provided separately on the opposite two sides and the pair of coolant discharge passages are provided separately on the opposite two sides, it is possible to supply the coolant uniformly and reliably to the entire coolant flow field.